Spin Delocalization and Vibrational–Electronic Interaction in the Toluene Ion–Radicals

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Abstract
An analysis is made of the spin distribution and hyperfine splittings of the toluene anion and cation radicals. Considered are the importance and magnitude of the splitting of the benzene-ion degeneracy by the interaction between the ring and the methyl group, the effects of spin delocalization into the methyl group by different mechanisms, and the consequences of vibrational and thermal coupling of the near-degenerate levels. The spin delocalization mechanism in the toluene ions is shown to be in agreement with a perturbation model for the Ċ–B = A system (here Ċ corresponds to the aromatic ring). The vibronic calculation is based on an ASMO–CI treatment of the electronic energy levels and their variation with bond lengths and angles; an attempt is made to include all significant vibrational contributions. The previously neglected alteration of the neutral-molecule vibrational functions due to the addition or removal of a pi-electron is found to be of particular importance. Although the exact quantitative results are dependent on the electronic parameters, the lowest anion vibronic state consists of about 90% of the antisymmetric and 10% of the symmetric electronic state. Comparison of the calculated and experimental temperature dependence of the anion hyperfine splittings shows that the vibronic treatment gives reasonable results.

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